Top seed Roger Federer [Images] withstood a few anxious moments before defeating Spain's Feliciano Lopez in four sets to book a quarter-final berth against old foe Andy Roddick [Images] at the U.S. Open on Monday.

The 60th-ranked Lopez won the first set in 24 minutes, firing 11 winners in a dazzling display of serving and sharply angled groundstrokes, but the Swiss maestro stepped up several gears to win their fourth-round match 3-6 6-4 6-1 6-4.

In the quarterfinals, Federer will play 2003 champion Roddick, the man he beat in last year's final, who was leading 7-6 2-0 when ninth-seeded Czech Tomas Berdych retired with nausea and breathing problems in their fourth-round clash.

The American said he felt sorry for Berdych but with a world number one Federer waiting in the wings, he added: "This is a lot better than being dead tired."

Haas upset sixth-seeded American James Blake 4-6 6-4 3-6 6-0 7-6, winning the tiebreaker 7-4, while Davydenko continued his march through the draw with a 6-1 6-3 6-4 rout of South Korea's Lee Hyung-taik.

Davydenko, who will face Haas in the quarters, has not lost a set during his four Open matches.